Until recently, transformation hardening of metals, primarily irons and steels having a minimum carbon content of approximately 0.2%, has been done primarily using induction heating techniques. More recently, lasers, particularly highpower CO.sub.2 lasers, have begun to replace induction-hardening and other case-hardening techniques, where minimum distortion and/or selective hardening of the workpiece is desired. An example of utilization of a laser for heat treating applications is U.S. Pat. No. 3,957,339.
Deficiencies exist with state of the art laser heat treating techniques. Existing laser heat treating, like the induction heat treating, often results in stressed or distorted parts. Where the applied heat from the laser is at power densities which are too low, optimum heat treating does not take place. Where power densities are maintained too high or for excessive time periods, distortion and melting takes place. This requires postheat treat straightening and machining. This is quite expensive and time consuming.
Nor does the known prior art laser heat treating provide for pre-conditioning of workpieces to optimally couple laser energy from the laser to the workpiece. Additionally, little attention has been given to a problem of optimum heat treating of cylindrical workpieces such as small diameter shafts and axles.